fastCGI on windows XP

I installed PHP on my Windows XP system using the Web Platform Installer (and probably somewhere choose to use 'FastCGI' as I had read this was the preferred way.) Under IIS 7.0, a simple PHP script produced an error "500.0 Internal Server Error'; detailed underneath as an error in the FastCGI Module. The Trace-log file of IIS confirmed this and added 'Not a valid win32 application'.
Although I spent hours searching (and noted lots of people have a problem 'something like this'), I can't find a solution or even a way to go forward. I would be most grateful for a hint on how to proceed.
Here is what I did so far: On some forum I found the suggestion to use Dependency Walker on the file php-cgi.exe and sure enough it found some files missing. First, some C++ libraries; this issue I solved using a download from Microsoft.
The error remained the same, though, and Dependency Walker is still missing two files: wer.dll and ieshims.dll. I don't know how to repair this (downloading separate dll's  doesn't seem a good idea) and in many forum answers to the same problem (missing these two particular files when using Dependency walker) are given the advice that this is a 'fake' problem which should be ignored.
Meanwhile, I've been looking for an answer to this question: when I execute php-cgi.exe directly (I mean: double-clicking it with windows explorer) it gives the error "Not a valid win32 application". Is it supposed to do that? And if not, how could I proceed? (By the way: php-win.exe gives the same error)
And if the error occurring when I directly execute php-cgi.exe is nothing to worry about - what, then, could be the problem?